In principle, there are two alternative possibilities of mounting an adjustment ring on the blade bearing ring for variable turbine and/or compressor geometries. The first possibility is a slide bearing, which may be simple to produce in terms of production engineering, but requires comparatively large actuation forces. The other possibility to this end is the so-called roller bearing, in which the adjustment ring is mounted on the blade bearing ring via a plurality of rollers. The latter method may allow comparatively low positioning forces to be realized, but the technical realization of such a roller-mounted variable turbine and/or compressor geometry is in turn comparatively elaborate and thus expensive as well.
A variable turbine and/or compressor geometry for an exhaust-gas turbocharger of the type in question with a generic blade bearing ring, on which individual guide blades are mounted in a rotatable manner, is known from DE 102 62 006 B4. Additionally provided is an adjustment ring for simultaneously adjusting the individual guide blades, wherein the positioning ring is in operative connection with adjusting levers of the guide blades. Mounting of the adjustment ring thereby ensues on the blade bearing ring via rollers. Said rollers per se have axial extensions produced integrally therewith, which are inserted in appropriate bores in the nozzle ring and/or in a housing section, where they are mounted in a freely rotatable manner. Here, the axial extensions have a diameter that is smaller than the diameter of the actual rollers. Such a variable turbine and/or compressor geometry is comparatively elaborate to produce, as corresponding bores are inserted in the nozzle ring and/or in the housing and the individual rollers also need to be individually mounted. A further great disadvantage is the fact that the variable turbine and/or compressor geometry cannot be produced as a pre-assembled unit with blade bearing ring, rollers, guide blades and adjustment ring and installed in the turbine housing as a unit.
A variable turbine and/or compressor geometry for an exhaust-gas turbocharger in which the adjustment ring is, however, mounted via a slide bearing relative to the blade bearing ring, is also known from U.S. Pat. No. 7,406,826 B2.